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"The source of seismic activity in the ETSZ is not known. The ETSZ is located far from edge of the North American continent and represents a mid-continent or intraplate earthquake zone. The known faults in the ETSZ are generally ancient; no known active faults reach the surface."
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From the Wikipedia article on the Eastern Tennessee Seismic Zone: en.m.wikipedia.org/wiki/Eastern_Tennessee_Seismic_Zone
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Desktop version of the link: en.wikipedia.org/wiki/Eastern_Tennessee_Seismic_Zone